/in/foo.cc: In function 'int main()':
/in/foo.cc:18:24: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for (int j=0; j<v[i].size(); j++) {
                       ~^~~~~~~~~~~~
/in/foo.cc:28:24: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for (int j=0; j<v[i].size(); j++) {
                       ~^~~~~~~~~~~~